Centralized traffic controlling system for railroads



Aug; 24, 1937. N. D. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS- Filed Feb. 17, 1933 Patented Aug. 24-, 1937 UNHED STATES CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Neil B. Preston, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application February 17, 1933, Serial No. 657,279

17 filaims.

This invention relates to railway centralized trafiic controlling systems, and more particularly to a system of the non-coded or direct control type, as distinguished from a selector type of sys- 5 tem.

It is proposed, in accordance with the present invention, to provide a means for controlling a remote power operated track switch by selecting the polarity or" energy applied at the control point to one line circuit, and to control the movement of traific over this switch by selecting the polarity of energy applied to a second line circuit. It is also proposed to provide a means for indicating over these same two line circuits the response of the track switch to the transmitted control, the

condition of the trafiic such as whether a signal is clear or stop and the particular direction of traffic set up when such a signal is clear, and also the presence of a train in a particular sec-- tion of track. It is further proposed to provide such interlocking of the circuits in the coinmunication of controls and indications that the transmission of conflicting controls is prevented and yet retain sufficient operating flexibility to permit efficient governing of trailic movements.

Other objects, purposes and characteristic features of the invention will appear as the description thereof progresses, during which references will be made to the accompanying drawing which illustrates in a diagrammatic and conventional manner one specific embodiment of the present invention, and which is susceptible of considerable modifications or adaptations in practice depending on the type of controls re quired and the character and number of indications which are considered advantageous in the particular application.

In the accompanying drawing, a complete communicating system is shown for transmitting controls and indications between a typical out lying field station and the apparatus at the control ofiice which is associated with this field station. It is to be understood, however, that in a practical application of this system there will be considerable distance between a field station and the control ofiice, and that it is necessary to ex tend only. three line wires over distance, namely wires L L and C. The wire C may he the common wire for the complete centralized trafiic controlling system, if so desired, or may be the common wire only for one station. In systems having several outlying field stations, two line wires such as L L will of course be required for each, and the field station apparatus as well as the control office apparatus which are designated by the legend on the drawing will also be duplicated for each oi the outlying stations.

A portion of a track diagram, which is asscciated with the typical section of track to which this invention is applied, is diagrammatically shown in the accompanying drawing with an indicating light OS of the conventional type arranged to display an indication of the presence of train in a particular track section. Similar indicating lights ESK and WSK are shown to simulate the actual signals which govern traffic over the outlying track switch.

A signal control lever SGL is employed to set up the controls for wayside signals governing trafiic over the track switch, and is operable to three positions, namely west, stop and east, indicated respectively by the reference characters W, S- and E. Suitable contacts are shown in the conventional manner as operated by the signal lever SGL. A switch control lever SNLL is operable to either of two positions for setting up controls for a switch machine employed to position a track switch in either its normal or reverse position. An indicating light COR is shown, as associated with the switch control lever SIVE, for indicating when the operated position of the track switch is in correspondence with the position of the switch control lever SML.

The section of track corresponding to the por tion of the track diagram shown at the control office is illustrated at the field station as includ" ing a track switch TS arranged to route trafiic over a main or diverging track. This track switch TS is operated by a switch machine SM when is in turn controlled by a two-position polar relay WZ. Suitable wayside signals ES, WS and WSA are shown in the conventional manner as governing trafilc movements over the track switch TS, and these signals are selectively cleared to govern traflic and its direction by the position of a three-position polar relay SZ. The position of the track switch TS as reflected by the relay WP may be arranged to select between the clearing of signals WS and WSA in the conventional manner, and a high and low speed signal at ES may be likewise selected.

Various other relays at both the control o-ffice and field station are shown in the conventional manner, and it may be here mentioned that the relay TK at the control oince is of the double winding type arranged so that one or the other of these windings is energized depending upon the position of the switch control lever SML and by relatively opposite polarities, but these windings are so arranged that the magnetism in the relay remains the same regardless of the polarity of energization, and this energizatio-n is maintained during a change of position of the lever SML by an operlapping lever contact as shown. The relays SK and WK at the control office are of the three-position polar type, and other neutral relays at both the control ofiice and at the field station have their operating characteristics designated by their base lines, or that is the relay WI at the field station is shown with a heavy base line to indicate that its drop-away time is considerably longer than other relays which are not shown in this manner.

The relays WM and EM at the field station are the conventional west and east signal repeating relays arranged in the local signalling circuits (not shown) to be normally energized whenever their associated signal is at stop but to be tie-energized whenever the associated signal displays a clear indication. The relay TR is the conventionally arranged track relay associated with a normally energized section of track including the track switch TS, and the relay WP is a conventional switch repeating relay arranged to operate its polar contacts to positions corresponding to the operated positions of the track switch TS and to drop its neutral contacts whenever the switch is not in either extreme locked position by circuits including point detector contacts such as shown in the patent to C. S. Bushnell No. 1,517,236 granted November 25, 1924.

In pointing out the circuits throughout the description of the operation of the present system, and will be considered opposite terminals of a source of energy at the control office and also of a similar source of energy located at the typical field station, while (0) will be considered a center or intermediate tap for each of these energy sources. It is also to be 3 understood that the common line wire C is connected to the center tap (c) of both the control fiice source of energy and the field station source of energy.

Operation In the accompanying drawing, the track switch TS is shown in its normal position for routing traffic straight through on the main track which is in accordance with the normal position N of the switch control lever SML thereby maintaining the relay CO at the control office energized by an obvious stick circuit completed by contact 3 of the lever SML in its normal position N and the front stick contact 4 of relay CO. The pick-up circuit for this correspondence relay G0 which is arranged to check the correspondence between the position of the control lever SML and the operated position of the switch TS will be fully described later.

Operation of track switch.It will first be considered, in describing the operation of the system, that an operator, desiring to reverse the track switch TS to route traffic upon the passing siding, moves the switch control lever SML to the position R thereby reversing the polarity on the switch control relay WZ at the field station over a circuit from (c) through the windings of relay WZ, wire 5, front contact 6 of relay EM, front contact T'of relay WM, front contact 8 of relay TR, line wire L back contact 9 of relay SL, wire iii, contact ll of lever SML in its reverse position R, wire l2, through the upper winding of relay TK to As soon as the lever SML is shifted from its normal position N to its reverse position R, the stick circuit for the relay CO is momentarily opened by the lever contact 3, which relay CO being quick acting then drops and its stick contact t prevents the reverse position of the lever contact 3 from again effecting its energization over this stick circuit. An indication that the position of the track switch TS is now out of correspondence with the position of the lever Sm is given by energization of the light COR overan obvious circuit completed at back contact l3 of. relay CO.

The polarity of the energy applied to the switch control relay WZ by the reverse position R of the switch control lever SML causes current to flow from right to left through its operating winding, which direction it will be considered operates its polar contacts to their extreme left hand positions which are then out of correspondence with the position of the contact of the switch repeating relay WP. A circuit for energizing the relay W1 is then completed by the out-of-correspondence condition between the contacts of relays W2 and WP (-1-), neutral front contact M of relay WP, wire l5, polar contact iii of relay W'P in its right hand position, wire l1, contact 18 of relay WZ in its left hand position, wires l9 and 20 and through the windings of relay WI to The left hand position of contact 22 of relay WZ is now effective to operate the switch machine SM over the reverse control wire RC in a manner to move the track switch TSto its reverse position thereby effecting the shifting of the contacts of relay WP to their left hand position by circuits not herein shown in detail. It is to be understood however that suitable approach locking means is to be provided in the control circuits for the switch machine SM, but in order to simplify the present disclosure, such locking means has been omitted from the drawing. It was previously stated that the neutral back contacts of relay WP are closed whenever the track switch TS is not in either extreme locked position, and consequently during a change in position of the track switch, the back contact 14 of relay WP is effective to maintain the energization of relay WI over an obvious circuit.

It is obvious that the positions of the contacts of relay WP are now in correspondence with the positions of the contacts of relay WZ thereby opening the energizing circuit for relay WI, but in as much as the releasing operation of this relay is considerably retarded, a period of time exists before its contacts drop, in which period, a circuit is completed which positions the contacts of relay WK at the control oflice in accordance with the position of the switch TS. This circuit may be traced from (c) through the windings of relay WK, wire 24, back contact 25 of relay CO de-energized, line wire L front contact 26 of relay TR, wire 21, front contact 28 of relay WI energized, wire 29, contact 30 of relay WZ in its left hand position, wire 3|, contact 32 of relay W'P in its left hand position, wire 33, neutral front contact 34 of relay WP, wire 35, polar contact 36 of relay WP in its left hand position to Current flowing from left to right through the windings of relay WK in this manner operates its contacts to their right hand positions which completes a circuit for energizing relay CO from contact 31 of relay WK in its right hand position, wire 38, contact 39 of the control lever SML in its reverse operated position R, Wires 40 and 4!, through the operating windings of relay CO to The relay CO picking up de-energizes the light COR. at back contact l3 thereby indicating that the position of the track switch TS is now in correspondence with the position of its control lever SML, and after the relay CO has thus become energized, the relay WI at the field station drops to de-energize relay WK at the control office by opening the line circuit at front contact 28, but the stick circuit completed by contact 3 of lever SML in its reverse position R is again effective to hold up relay CO.

If a condition should exist wherein the switch control lever SML is returned to its original position before the switch had operated into correspondence with the previously transmitted control but had become unlocked, a correspondence indication could not be transmitted to the control office because the previously traced indicating circuit would then be open at front contact 34 of relay WP. It will be obvious from this description of the operation of the system to indicate the response of the switch TS to the transmitted control that the releasing time of relay WI at the field station must exceed the cumulative pick-up times of relays WK and CO for proper operation.

Signal controZ.Considering now that the operator desires to allow a train movement from the main track eastward onto the diverging track, the signal control lever SGL is moved to its clear east-bound position E. A circuit is then completed which positions the contacts of the signal control relay SZ at the field station to the left and picks up the series relay SL at the control ofiice, which circuit may be traced from (c) through the windings of relay SZ, wire 43, back contact 28 of relay WI, wire 21, front contact 26 of relay TR, line wire L front contact 25 of relay CO, wire 44, through the windings of relay SL, wire 45, contact 46 of the signal controllever SGL in position e to The series line relay SL at the control office now picks up to open the switch control circuit over line wire L and to shift this line circuit over line wire L to include the signal indicating relay SK at the control office, and the current flowing through the signal control relay SZ from right to left operates the polar contact 41 to its left hand position thereby being effective to clear the east bound signal ES over circuits not shown in detail .but merely indicated by the dotted line.

As soon as the signal ES clears, the relay EM which is associated with this direction of traffic drops, as previously described, thereby completing a circuit for distinctively positioning the relay SK at the control office, which circuit may be traced from back contact 6 of relay EM, front contact I of relay WM, front contact 8 of relay TR, line wire L front contact 9 of relay SL, wire 48, through the winding of relay SK to An indication that the signal ES is displaying a clear indication is now given at the control office by energizing the indicating lamp ESK from contact 49 of relay SK in its left hand position, wire 50, through the indicating lamp ESK to The manner in which a west bound signal WS may be cleared from the control oifice is obvious from the foregoing description, or, if the signal lever SGL is operated to the clear west-bound position W, an opposite polarity is placedon the line circuit over wire L thereby positioning the contacts of relay SZ to the right. The contact M of relay SZ in its right hand position is obviously effective to clear the west bound signal 0 WS which then effects the dropping of relay WM to apply the reverse polarity to the signal indicating relay SK at the control ofiice over line wire L or that is, contact 49 of relay SK will be operated to its right hand position, which obviously completes a circuit for energizing the indicating lamp 'WSK. It is also obvious that the signal control circuit previously traced over line wire L is only completed when the relay WI at the field station is de-energized and when the relay CO at the control office is energized, and

consequently if some abnormal condition exists in which the switch TS is either operated out of correspondence with the control relay WZ or is in a mid-stroke position, it is impossible to register a clear signal control at the field station because relay WI will be energized either by the out-of-correspondence contacts l6 and I8 of reswitch TS thereby dropping the relay TR, and

opening both line wires L and L at front contacts 8 and 26 thereof respectively. The opening of line wire L obviously drops. relay SL at the control oflice, and in as much as the relay TK is already dropped while the relay SL was previously energized, it cannot again pick up when is also opened by the dropping of the track relay TR. An indication of the occupancy of the track section at the field station is now given at the control office by energizing the indicating light OS over a circuit from back contact 52 of relay SL, wire 53, back contact 54 of relay TK, wire 55, through the indicating light OS to It will be obvious that when the track relay TB is dropped both the east bound or the west bound signals will be placed at stop over the local signalling circuits thereby causing relay EM and WM to be energized and the indication of the clear signal at the control office will be extinguished by the de-energization of relay SK which opens the indicating circuits at contact 49 in its tie-energized position. As soon as the train progresses out of the track section governing the relay TR, the system will again return to its normal condition as determined by the position of the control levers SGL and SML and the indicating light OS will be de-energized by back contact 52 if the signal control lever SGL is allowed to remain in a clear position to pick up relay SL, or if it is moved to a stop position S, the relay SL will not pick up thereby allowing the relay TK to be energized and to open the energizing circuit for the indicating lamp OS at back contact 54.

contact 9 of relay SL drops because line wire L Y A railway centralized traffic controlling system has thus been provided which permits the control of a distant track switch by selecting the polarity of energization of one line circuit including a single line wire and a common wire. This line circuit is normally maintained energized with this selected polarity from anenergy source at the control point, but when the switch control lever is changed to a new position, a stick circuit normally holding up a switch correspondence relay is momentarily interrupted by a lever contact thereby causing its de-energization which effects the display of an indicationthat the posi-- control, the slow releasing relay is de-energized,

but during the-time consumed in dropping, an

impulse of energy is applied to the second line circuit of a polarity corresponding to the switch position thereby momentarily positioning a switch indicating relay at the control ofiice which energizes a switch correspondence relay providing theposition of the switch indicating relay corresponds to the position of the switch control lever. The previously mentioned stick circuit then holds up the correspondence relay until a subsequent change in position of the switch control lever, and this correspondence relay serves to indicate the response of the switch as well as to condition the second line circuit at the control ofiice for the transmission of a signal control, and at the field station, this second line circuit is likewise conditioned for such signal control by the dropping of the slow releasing relay.

A signal governing movements in either direction over the track switch may now be selectively cleared by applying either of two polarities of energy to the second line circuit in accordance with the position of a signal control lever. The

second line circuit, now conditioned for signal control energy, includes a series relay at the control office which picks up with the application of such signal control energy to shift the first line circuit to include a signal indicating relay at 0 the control ofiice, and when the signal has responded to the transmitted control, this first line circuit is energized at the field station with a polarity distinctive of the governing direction of the clear signal.

A means for indicating the presence of a train on a track section associated with the distant track switch has also been provided by opening both the previously mentioned line circuits at the field station due to the dropping of a conventionally arranged track relay, which opening is effective at the control oiiice to drop the relay in series with the second line circuit as well as a relay in series with the first line circuit, thereby controlling an indicating means over a circuit ineluding contacts of each relay in series.

The above rather specific description of one form of the present invention is given solely by way of example, and is not intended in any manner whatsoever in a limiting sense. It is also to be understood that various modifications, adaptations and alterations may be applied to meet the requirements of practice without in any-manner departing from the spirit or scope of the present invention, except as limited by the appended claims.

Having thus described my invention, what I claim is:

1. In a railway centralized traific controlling system, a control office, a distant field station, a 60 first and a second line circuit each connecting said control oifice and said field station, a switch control lever at said control ofiice arranged to control the operation of a track switch at said field stationover said first line circuit, a stick relay at 65 said control office, a stick circuit for said stick relay arranged to be de-energized by a change in position of said switch control lever, means for energizing said second line circuit in accordance with the operated position of said track switch, a pick up circuit for said stick relay, and means at the control office for momentarily energizing said pick up circuit of said stick relay only if the energization of said second line circuit corresponds to the position of said switch control 75 lever.

2. In a railway trafiic controlling system, a control office, a distant track switch and associated signals, two line circuits connecting the control ofiice with the track switch and signals, a switch control lever at the control ofiice arranged to control the operation of said track switch over a first of said line circuits, a stick relay at the control oflice arranged to be de-energized by a change in position of said switch control lever, means for only momentarily energizing the second of said line circuits in accordance with the operated position of said track switch, means for initially energizing said stick relay only if said momentary energization of the second line circuit corresponds to the position of said switch control lever, and means for selectively clearing said signals only when said stick relay is energized.

3. In a railway trafiic controlling system, a control ofilce, a distant track switch and associated signals, two line circuit means connecting the control ofiice with the track switch and signals, a switch control lever at the control office arranged to control the operation of said track switch over a first of said line circuit means, a stick relay at the control ofiice arranged to be de-energized by a change in position of said switch control lever, means for momentarily energizing the second of said line circuit means in accordance with the operated position of said track switch, means for energizing said stick relay if said momentary energization of the second line circuit means corresponds to the position of said switch control lever, means for selectively clearing said signals over the second line circuit means When said stick relay is energized, and means for energizing the first line circuit means in accordance with a clear signal when the second line circuit means is energized.

4. In a railway traffic controlling system, a control office, a distant field station, a first line circuit means connecting the control office and the field station, a track switch control means at said field station positioned according to the polarity of energy applied at said control ofiice to said first line circuit means, a second line circuit means connecting the control office and the field station, means to only momentarily condition said second line circuit means for transmitting indications to the control office when the polarity of energization of said first line circuit means is changed, means in said control ofiice for registering the indications transmitted over said second line circuit means, and means for transmitting controls to the field station over said sec ond line circuit meansonly after said indications have been registered at the control ofiice.

5. In combination, a control ofilce, a field station, a normally energized line circuit including one line wire connecting the control office and the field station, means for controlling a track switch at the field station in accordance with the polarity of energization of said line circuit, a normally de-energized line circuit including a second line wire connecting the control ofiice and the field station, means at the field station for momentarily energizing said normally de-energized line circuit with a polarity corresponding to the position or said track switch, a signal control means at said control office, storing means at said control office responsive to said momentary energization of said normally deenergized line circuit and arranged to condition a third line circuit including said second line wire to be selectively energized'by said signal control means at said control ofiice, and means at said field. station responsive to energy applied to said third line circuit for controlling a signal at the field station.

6; In combination, a control office, a field station, a first line circuit means connecting the control ofiice and the field station, means for controlling a track switch at the field station over said first line circuit means, a second line circuit means connectingthe control office and the field station, means for clearing either of two signals at the field station by selecting the polarity of energization of said second line circuit means at the control oflice, means for connecting said first line circuit means to a signal indicating means at the control ofiice only when said second line circuit means is energized from said control office, means for energizing said first line circuit means at the field station with a distinctive polarity when one of said signals is clear, means for de-energizing said first and second line circuit means during an occupied condition of a track section at the field station, and indicator means at the control office responsive only to the deenergization of both said first and second line circuits to indicate said occupied condition.

'7. In combination, a control office, a field station, a first line circuit means connecting the control office and the field station, means for controlling a track switch at the field station over said first line circuit means, a second line circuit means connecting the control office and the field station, means for indicating at the control ofiice the operated position of said track switch by applying a distinctive polarity of energization to said second line circuit means at said field station, means at the control office and at the field station for rendering said second line circuit means capable of selectively clearing signals at the field station from the control oifice only when an indication of the operated position of said track switch has been registered at the control office, means for connecting said first line circuit means to signal indicating means at the control office only when said second line circuit means is energized at said control ofiice to clear said signals at said field station, means for energizing said first line circuit means at the field station when one of said signals is clear, means for de-energizing said first and said second line circuit means during an occupied condition of a track section at the field station, and indicator means at the control ofiice responsive only to the deenergization of both said first and second line circuits to indicate said occupied condition.

8. In combination, a control ofiice, a switch control circuit means connecting the control office and a distant track switch, a signal control circuit means connecting the control oifice and signals associated with said track switch, means for only momentarily rendering said signal control circuit means effective to transmit switch indications after each change in position of said track switch, indication storing means at the control office responsive to said momentary energization of said signal control circuit means in accordance with said switch indication and effective to continue the registration of such indication only so long as the control of said track switch is unchanged, and means -for rendering said switch control circuit means efiective to transmit signal indications when said signal control circuit means is energized from the control ofiice only provided said indication storing means registers the last'switch indication transmitted.

9. In combination; a switch machine for operating a track switch; a control lever having two extreme positions for governing the operation of said switch machine to either of two extreme positions; indication means including an indicator for indicating the position of said switch machine and the track switch; a stick relay; a pick up circuit for said stick relay closed only when and only momentarily each time said control lever and said indication means are operated into corresponding positons; a stick circuit for said stick relay including only the windings of said stick relay, its own front contact and a contact on said control lever closed only when said lever is in one or the other of its extreme positions; said indicator being energized when said stick relay is deenergized, whereby an indication is displayed each time said control lever is moved to a new position and the displayed indication is annulled each time said control lever, said switch machine and the track switch are operatswitch control relay and said switch position re peating relay are operated into corresponding positions; and means including said slow acting relay for causing the control of said relay means to be only momentary. 1

11. In a centralized traffic controlling system for railroads, a control ofiice and a field station connected by a first line circuit and a second line circuit respectively including first and second line wires, a track switch at said station, a switch machine and associated signals for governing traffic over said track switch, switch control means in said office. for transmitting a plurality of distinctive switch controls over said first line circuit, signal control means in said ofiice for transmitting a plurality of distinctive signal controls over said second line circuit, switch control means at said station responsive to said switch controls on said first line circuit for distinctively operating said switch maclfine, signal control means at said station responsive to said signal controls on said second line circuit for distinctively operating said signals, switch indicating means at said station for transmitting a plurality of distinctive switch indications over a third line circuit including said second line wire, signal indicating means at said station for transmitting a plurality of signal in dications over a fourth line circuit including said first line wire, means in said ofiice responsive to said switch indications on said third line circuit for controlling a switch indicating device, means in said office responsive to said signal indications on said fourth line circuit for controlling a signal indicating device, means responsive to the operation of said switch machine for momentarily shifting said second line wire from said signal control means at said station to said switch indication transmitting means, and means responsive only to the transmission of one of said signal controls over said second line circuit for shifting said first line wire from said switch control means at said ofiice to said signal indicating device at said office.

12. In a centralized traflic controlling system for railroads, a control oifice and a field station connected by a first line circuit and a second line circuit respectively including first and second line wires, a track switch at said station, a switch machine and associated signals for governing trafiic over said track switch, switch control means in said ofiice for transmitting a plurality of distinctive switch controls over said first line circuit, signal control means in said oflice for transmitting a plurality of distinctive signal controls over said second line circuit, switch control means at said station responsive to said switch controls on said first line circuit for distinctively operating said switch machine, signal control means -at said station responsive to said signal controls on said second line circuit for distinctively operating said signals, switch indication transmitting means at said station for transmitting a plurality of distinctive switch indications over a third line circuit, signal indication transmitting means at said station for transmitting a plurality of signal indications over a fourth line circuit, means in said office responsive to said switch indications on said third line circuit for controlling a switch indicating device, means in said oflice responsive to said signal indications on said fourth line circuit for controlling a signal indicating device, means responsive to the operation of said switch machine for momentarily shifting said second line wire from said second line circuit to said third line circuit controlled by said switch indication transmitting means, means responsive only to the transmission of one of said signal controls over said second line circuit for shifting said first line wires from said first line circuit to said fourth line circuit controlled by said signal indication transmitting device, means at said station for opening both of said line wires in response to the occupancy of the track section associated with said track switch, and means responsive to the-opening of both line wires for registering an OS indication at said ofiice.

13. In a centralized trafilc controlling system for railroads, a control ofiice and a field station connected by a line circuit, a switch machine at said station, a switch machine control relay having normal and reverse positions, a switch position repeating relay having normal and reverse positions, a slow acting relay, an energizing circuit for said slow acting relay completed when said repeating relay is in a normal or reverse position out of correspondence with the normal or reverse position of said control relay, means including a front contact of said slow acting relay and responsive to the operation of said switch control relay and said switch position repeating relay into corresponding positions for only momentarily energizing said line circuit from said station, and indicator means at said control ofilce responsive to momentary energization of said line circuit from said station.

14. In a centralized traflic controlling system for railroads; a power operated track switch; a switch control relay for governing the power operation of said track switch; a switch control lever for at times governing the operation of said switch control relay; a correspondence relay; pick up circuit means for momentarily energizing said correspondence relay when said switch control lever, said switch control relay and said track switch are in corresponding positions; and

stick circuit means for said correspondence relay including a contact momentarily opened by each movement of said switch control lever.

15. In the centralized traiiic controlling system for railroads; a power operated track switch; a signal for governing trafilc over said track switch; a switch control relay for governing the power operation of said track switch; a switch control lever for at times governing the operation of said switch control relay; a correspondence relay; pick up circuit means for momentarily energizing said correspondence relay when said switch control lever, said switch control relay and said track switch are in corresponding positions; stick circuit means for said correspondence relay including a contact momentarily opened by each movement of said switch control lever; and circuit means for clearing said signal only when said correspondence relay is picked up.

16. In a centralized traffic controlling system for railroads; a power operated track switch; a

control lever for at times governing the power operation of said track switch; a switch position indicating relay; a correspondence relay; circuit means for energizing said switch position indicating relay with one polarity or the other dependent upon the normal or reverse position of said track switch, said circuit means including a back contact of said correspondence relay; a pick up circuit for said correspondence relay closed whenever said switch position indicating relay indicates a position corresponding with the position of said switch control lever; and a stick circuit for said correspondence relay including a contact momentarily opened by each movement of said control lever.

17. In a centralized traific controlling system for railroads; a line wire connecting a control ofiice with a field station; a power operated track switch at the field station; a signal for governing traffic over said track switch; a switch control lever at the control oflice for governing the power operation of said track switch; a signal control lever at the control ofiice; a signal control relay at the field station for controlling said signal; a switch indication relay at the control office; a transfer relay at the field station momentarily picked up each time said switch control relay is operated out of correspondence with said track switch and whenever said track switch is in operation or is unlocked; a contact on said transfer relay for connecting the field station end of said line wire with said signal control relay when dropped away and for connecting said field station end of said line wire with switch position indicating contacts when picked up; a correspondence relay in the control office having a contact for connecting the control ofiice end of said line wire with said switch indication relay when deenergized and with said signal control lever when energized; pick up circuit means for said correspondence relay energized whenever said switch position indicating relay indicates said track switch to be in correspondence with said switch control lever; and stick circuit means for said correspondence relay including a contact of said switch control lever momentarily opened whenever said lever is operated to an opposite position, whereby said line wire is momentarily employed to transmit an indication of the position of said track switch each time it is operated to a new position and is thereafter available for the control of said signal.

NEIL D. PRESTON. 

